Expandable intervertebral implant

ABSTRACT

An expandable intervertebral implant is provided for insertion into an intervertebral space defined by adjacent vertebrae. The expandable intervertebral implant includes a pair of outer sleeve portions and an inner core disposed between the outer sleeve portions. Movement of the inner core relative to the outer sleeve portions causes the outers sleeve portions to deflect away from each other, thereby engaging the expandable intervertebral implant with the vertebrae and adjusting the height of the intervertebral space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.12/936,466 filed Oct. 5, 2010, which is a National Stage ofInternational Application Serial No. PCT/US2009/039501, filed Apr. 3,2009, which claims the benefit of U.S. Provisional Application Ser. No.61/042,724, filed on Apr. 5, 2008, the disclosure of each of which ishereby incorporated by reference as if set forth in its entirety herein.

FIELD OF THE INVENTION

This disclosure relates generally to intervertebral implants, and inparticular relates to an intervertebral implant that can expand tocreate a desired spacing and/or angular orientation of adjacentvertebrae.

BACKGROUND OF THE INVENTION

Degenerative disc disease or degeneration of a vertebral body oftenresults in a loss of disc height, which in turn can cause facet andnerve impingement, among other things. One standard of care is toreplace the damaged intervertebral disc with an intervertebral implantor a damaged portion or an entire vertebral body with an intervertebralimplant.

Thus, an intervertebral implant may be inserted into the intervertebraldisc space of two adjacent vertebral bodies or into the space created byremoval of portions of, or the entire, vertebral body after removal ofdamaged portions of the spine. Preferably, the intervertebral implantrestores the spine, as much as possible, to a natural state. That is,the implant preferably restores the original height of theintervertebral disc and thus the original distance between the twoadjacent vertebral bodies or vertebral bodies in various levels of thespine. These implants are sized and shaped to fill at least thephysiological height between the vertebral bodies and are insertedthrough a relatively narrow and small incision with nerves and vascularstructure proximate sides of the incision. Accordingly, it isadvantageous to develop an implant that may be inserted in a reducedsize or configuration and expanded when positioned between the vertebraeto minimize the required incision and limit the potential for theimplant to contact the neural and vascular structure duringimplantation.

It is desirable to construct an intervertebral implant that restores thespine to its natural state, is relatively compact during insertion andmay be expanded when positioned between adjacent vertebrae. It is alsodesirable to construct an expandable intervertebral implant that may beinserted and expanded utilizing the same instrument.

BRIEF SUMMARY OF THE INVENTION

The following Summary is provided to introduce a selection of conceptsin a simplified form that are further described below in the DetailedDescription of Illustrative Embodiments. This Summary is not intended toidentify key features or essential features of the invention, nor is itintended to be used to limit the scope of the invention. Reference ismade to the claims for that purpose.

Certain embodiments are directed to an expandable intervertebral implantfor insertion into an intervertebral disc space and expandable from aninitial position to an expanded position. The expandable intervertebralimplant includes a linkage that includes a plurality of links connectedin a longitudinal direction. Each link includes an outer sleeve having afirst outer sleeve portion and a second outer sleeve portion that ismovable with respect to the first outer sleeve portion. The second outersleeve portion defines a first engagement surface that is sloped withrespect to the longitudinal direction. Each link further includes aninner core disposed between the first and second outer sleeve portions.The inner core defines a second engagement surface that is sloped withrespect to the longitudinal direction, wherein the second engagementsurface abuts the first engagement surface. Relative movement betweenthe inner core and the second outer sleeve portion along thelongitudinal direction causes the first engagement surface to ride alongthe second engagement surface, thereby causing the second outer sleeveportion to deflect away from the first outer sleeve portion in adirection substantially perpendicular to the longitudinal direction.

Additional features and advantages will be made apparent from thefollowing detailed description of illustrative embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, isbetter understood when read in conjunction with the appended drawings.There is shown in the drawings example embodiments, in which likereference numerals correspond to like reference numerals throughout. Theexpandable intervertebral implant and related methods are not limited tothe specific embodiments and methods disclosed, and reference is made tothe claims for that purpose.

FIG. 1A is a perspective view of an expandable intervertebral implantconstructed in accordance with one embodiment installed in anintervertebral space;

FIG. 1B is a perspective view similar to FIG. 1A, but with theintervertebral implant installed in the intervertebral space inaccordance with an alternative embodiment

FIG. 2A is a sectional side elevation view of the expandableintervertebral implant illustrated in FIG. 1 constructed as a linkagethat includes a plurality of expandable intervertebral links inaccordance with one embodiment, wherein the implant is in a firstcontracted position;

FIG. 2B is an enlarged portion of the expandable intervertebral implantillustrated in FIG. 2A;

FIG. 3A is a side elevation view of an expandable intervertebral link ofthe intervertebral implant illustrated in FIG. 2A;

FIG. 3B is a side elevation view of the expandable intervertebral linksimilar to FIG. 3A, but constructed in accordance with an alternativeembodiment;

FIG. 3C is a side elevation view of the expandable intervertebral linksimilar to FIG. 3A, but constructed in accordance with anotheralternative embodiment;

FIG. 4A is a sectional end elevation view of the expandableintervertebral link illustrated in FIG. 3A;

FIG. 4B is a sectional end elevation view of an expandableintervertebral link similar to that illustrated in FIG. 4A, butconstructed in accordance with an alternative embodiment;

FIG. 5 is a sectional side elevation view of the expandableintervertebral link illustrated in FIG. 2A;

FIG. 6 is a sectional side elevation view of the expandableintervertebral implant illustrated in FIG. 5A, connected to an insertiondevice.

FIG. 7 is a sectional side elevation view of the expandableintervertebral implant illustrated in FIG. 6, but illustrated in asecond vertically expanded position;

FIG. 8A is a top plan view of the expandable intervertebral implantillustrated in FIG. 7, including a retainer that secures variouscomponents of the expandable intervertebral implant;

FIG. 8B is a sectional end view of the expandable intervertebral implantas illustrated in FIG. 8A;

FIG. 8C is an enlarged view of a portion of the expandableintervertebral implant illustrated in FIG. 8B;

FIG. 9A is a sectional end view of the expandable intervertebral implantsimilar to FIG. 8B, but showing a retainer constructed in accordancewith an alternative embodiment;

FIG. 9B is a side elevation view of the expandable intervertebralimplant illustrated in FIG. 9A;

FIG. 10 is a sectional side elevation view of an expandableintervertebral implant similar to FIG. 6, but configured to provide alordotic outer profile when expanded, in accordance with an alternativeembodiment;

FIG. 11 is a sectional side elevation view of the expandableintervertebral implant illustrated in FIG. 10, but showing the implantin a vertically expanded position;

FIG. 12A is a top plan view of the expandable intervertebral implantillustrated in FIG. 10;

FIG. 12B is an enlarged side elevation view of a portion of theexpandable intervertebral implant illustrated in FIG. 12A;

FIG. 13 is a side elevation view of an expandable intervertebral implantincluding a second retainer constructed in accordance with analternative embodiment;

FIG. 14 is a sectional side elevation view of an expandableintervertebral implant similar to FIG. 10, but configured to define alordotic outer profile when expanded, in accordance with an alternativeembodiment;

FIG. 15A is a top sectional view of an expandable intervertebral implantsimilar to that illustrated in FIG. 6, but further configured forlateral expansion in accordance with an alternative embodiment, whereinthe expandable intervertebral implant is shown in a laterally contractedposition;

FIG. 15B is a sectional end view of the expandable intervertebralimplant illustrated in FIG. 15A including a retainer constructed inaccordance with one embodiment;

FIG. 15C is a sectional end view of the expandable intervertebralimplant similar to FIG. 15B, but showing the expandable intervertebralimplant in a vertically and laterally expanded position;

FIG. 15D is a sectional end view of the expandable intervertebralimplant similar to FIG. 15C, but including a retainer constructed inaccordance with an alternative embodiment;

FIG. 16A is a side elevation view of an expandable intervertebralimplant coupled to a biasing member of an insertion device in accordancewith one embodiment;

FIG. 16B is a side elevation view of the expandable intervertebralimplant illustrated in FIG. 16A, but with the biasing member coupled toadditional components of the insertion device, wherein the insertiondevice is illustrated in a disengaged position;

FIG. 16C is a side elevation view of the expandable intervertebralimplant as illustrated in FIG. 16B, but showing the insertion device inan engaged position;

FIG. 17A is a side elevation view of the expandable intervertebralimplant as illustrated in FIG. 16C, but showing the insertion deviceincluding a central sleeve having a coupling member that locks theinsertion device in the engaged configuration;

FIG. 17B is a side elevation view of the central sleeve illustrated inFIG. 17A;

FIG. 17C is a top plan view of the central sleeve illustrated in FIG.17B;

FIG. 18A is a top plan view of an expandable intervertebral implantcoupled to an angulated insertion device constructed in accordance withan alternative embodiment;

FIG. 18B is a top plan view of the expandable intervertebral implantcoupled to the angulated insertion device illustrated in FIG. 18A,showing the insertion device in an angulated position;

FIG. 19A is a sectional side elevation view of an expandableintervertebral implant shown in an expanded position; and

FIG. 19B is a sectional side elevation view of the expandableintervertebral implant illustrated in FIG. 19A, but showing projectingportions removed after the implant has achieved the final expandedposition.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inwardly” or “distally” and “outwardly” or “proximally” refer todirections toward and away from, respectively, the geometric center ofthe expandable implant, instruments and related parts thereof. Thewords, “anterior”, “posterior”, “superior,” “inferior” and related wordsand/or phrases designate preferred positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

Referring to FIG. 1A, an expandable intervertebral implant 20 is showninstalled into an intervertebral disc space 22 defined by a pair ofadjacent, or neighboring, upper and lower vertebrae 24. The expandableintervertebral implant 20 can be configured to fuse with the vertebrae24. The vertebrae 24 can be lumbar vertebrae that define an anteriorside AS, an opposing posterior side PS. The vertebrae 24 further defineopposing lateral sides LS that are disposed on opposing sides of acentral medial axis M-M that extends along a mediolateral direction. Thevertebrae 24 are illustrated as being spaced along a caudocranial axisC-C. The expandable intervertebral implant 20 extends generally along alongitudinal direction L, a lateral direction A, and a transversedirection T.

Various structure is therefore described as extending horizontally alonga longitudinal direction “L” and lateral direction “A”, and verticallyalong a transverse direction “T”. The housing is elongate in thelongitudinal direction L. Unless otherwise specified herein, the terms“lateral,” “longitudinal,” and “transverse” are used to describe theorthogonal directional components of various components. The directionalterms “inboard” and “inner,” “outboard” and “outer,” and derivativesthereof are used herein with respect to a given apparatus to refer todirections along the directional component toward and away from thegeometric center of the apparatus.

It should be appreciated that while the longitudinal and lateraldirections are illustrated as extending along a horizontal plane, andthat the transverse direction is illustrated as extending along avertical plane, the planes that encompass the various directions maydiffer during use. Accordingly, the directional terms “vertical” and“horizontal” are used to describe the expandable intervertebral implant20 and its components as illustrated merely for the purposes of clarityand illustration.

In the illustrated embodiment, the longitudinal direction L extends inan anteroposterior direction, the lateral direction A extends in themediolateral direction, and the transverse direction T extends in thecaudocranial direction. It should be appreciated, however, that thedirections defined by the expandable intervertebral implant 20 couldalternatively be oriented at any desirable angle between 0° and 180°with respect to the various directions defined by the vertebrae 24. Forinstance, the longitudinal and lateral directions of the implant couldbe oriented at any desirable angle between 0° and 180° with respect tothe mediolateral and anteroposterior directions. As will becomeappreciated from the description below, the expandable intervertebralimplant 20 can be inserted into the disc space 22 in an anteriordirection, a posterior direction, or any alternative direction between0° and 180° with respect to the anterior and posterior sides.

For instance, FIG. 1B illustrates the expandable intervertebral implant20 installed into the intervertebral space 22 in an orientation that is180° rotated with respect to the orientation illustrated in FIG. 1A. Inthis regard, it should be appreciated that the implant 20 can beinserted into the intervertebral space 22 from the anterior or posteriordirection, or a direction that is angularly offset from the anterior orposterior direction. When inserting the implant 20 into theintervertebral space 22, for instance from the posterior, posterioranatomical elements can be removed, such as ligaments, a part or all ofthe lamina, the posterior arch, and some or all of the facet joints thatare aligned with the vertebral space that receives the implant. Whileone implant 20 is illustrated as being inserted into the intervertebralspace 22 in FIG. 1A, and a pair of implants 20 as being inserted intothe intervertebral space 22 in FIG. 1B, any desired number of implants20 can be inserted into a given intervertebral space as desired, such asbetween one and four implants. It should further be appreciated that oneor more implants 20 can be installed into the intervertebral space 22when performing a corpectomy or hemicorpectomy.

Referring now to FIGS. 2A, 3A, and 4A, the expandable intervertebralimplant 20 can be provided as a longitudinally elongate linkage 26 thatincludes one or more links 28. The implant 20 can be made from anysuitable biocompatible radiolucent or metallic material, such astitanium. The links 28 of the linkage 26 can be substantially similarlyor identically constructed unless otherwise indicated. Each linkincludes an outer sleeve 30 formed from a pair of vertically opposingupper and lower outer sleeve portions 30A and 30B. The outer sleeveportions 30A and 30B each define a laterally elongate cross-beam 31connected to a pair of outer legs 33 that each project transverselyinward from the opposing outer lateral ends of the cross beams 31. Thus,the upper sleeve portion 30A includes legs 33 that project down from thelaterally outer ends of the corresponding cross-beam 31, and the lowersleeve portion 30B includes legs 33 that project up from the laterallyouter ends of the corresponding cross-beam 31. When the link 28 is in afirst or initial contracted position, the inner transverse ends of thelaterally aligned legs 33 can abut each other as illustrated so as tominimize the height of the implant 20 prior to installation into theintervertebral space 22, or they can alternatively be spaced apart.

The cross-beams 31 can each define respective vertebral engagementsurfaces 32, such that the vertebral engagement surface of the uppersleeve portion 30A is an upwardly-facing surface, and the vertebralengagement surface of the lower sleeve portion 30B is adownwardly-facing surface. Each vertebral engagement surface 32 isconfigured to abut the corresponding upper and lower adjacent vertebrae24.

Each outer sleeve portion 30A and 30B can include a plurality of teeth34 projecting transversely out from the respective vertebral engagementsurfaces 32. The teeth 34 can be laterally elongate, and can be arrangedas a plurality of longitudinally spaced rows 36 as illustrated. Theteeth 34 can have a substantially constant height across the pluralityof rows 36, thereby defining a substantially linear toothed profile asillustrated in FIG. 3A. Alternatively, the teeth 34 can define anonlinear profile across the rows. For instance, as illustrated in FIG.3B, the rows of teeth of one or more links 28 can define a bowedprofile, or a convexity, whereby the teeth 34 of the longitudinallymiddle rows have a height greater than the teeth of the longitudinallyouter rows. The profile can be symmetrical or asymmetrical about alateral axis passing through the longitudinal midpoint of the link 28.

Alternatively or additionally, referring to FIG. 4A, one or more of therows 36 of teeth 34, up to all of the rows of teeth, can be bowed alongthe lateral direction, such that the laterally middle portions of theteeth 34 have a height that is greater than the laterally outer portionsof the teeth. The profile can be symmetrical or asymmetrical about alongitudinal axis passing through the lateral midpoint of the link 28.Thus, the teeth 34 can define a profile that is convex, or bowed, alongmore than one direction. While the teeth 34 are shown as being laterallyelongate, it should be appreciated that the teeth 34 can alternativelybe discontinuous in a lateral direction across the vertebral engagementsurfaces 32 in a lateral direction. For instance, referring to FIG. 4B,a second plurality of teeth 34 can project out from the vertebralengagement surfaces 32 along the lateral direction. Thus each row 36 mayinclude one or more teeth 34 so as to form an array of laterally spacedand longitudinally spaced teeth 34 along the vertebral engagementsurfaces 32. The teeth 34 can be in substantial vertical alignment alonga lateral axis, or can be bowed as shown in FIG. 4B to define a convexprofile along the lateral direction such that laterally central teeth 34have a height greater than that of the laterally outer teeth of a givenrow 36. Alternatively or additionally, the teeth 34 can be bowed asshown in FIG. 3B to define a convex profile along the longitudinaldirection.

The teeth 34 can assist in roughening the vertebral surface to assist infusing the expandable intervertebral implant to the adjacent vertebrae,can provide a surface that grips against the vertebrae, and can alsodefine an increased surface area that fuses with the adjacent vertebraewith respect to a flat vertebral engagement surface. Alternatively, oneor both of the opposing vertebral engagement surfaces 32 can besubstantially smooth, or non-toothed, along both the lateral andlongitudinal directions, as illustrated in FIG. 3C. The smooth surfacecan extend substantially along a longitudinal-lateral plane, or can bebowed in either or both of the lateral and longitudinal directions.

With continuing reference to FIG. 2A, the linkage 26 can include one ormore links 28, such as a plurality of adjoined links 28 as illustrated.Each link 28 can include a lateral cross beam 31 and a pair of opposingtransverse legs 33 in the manner described above. Each link 28 candefine a generally rectangular or square with straight or curvedcorners, edges, and surfaces, or any suitable alternative geometricshape. The linkage 26 defines a longitudinal front end 27 and anopposing longitudinal rear end 29. The rear end 29 of the linkage 26 canbe geometrically configured for insertion into the intervertebral discspace 22. For instance, the cross beams of the link 28 disposed at therear end 29 of the linkage can be curved transversely inward along adirection from front end 27 toward the rear end 29, thereby providing aguide surface when inserting the implant 20 into the intervertebral discspace 22.

Adjacent links 28 can be integrally connected or can alternatively bediscreetly fastened to each other at a coupling location using anysuitable mechanical or adhesive coupling member. For instance, acoupling member 35 can project longitudinally out from each leg 33 ofadjacent links 28 toward the adjacent link 28, such that a couplingmember 35 of the upper sleeve portion 30A of one link 28 is attached toa corresponding coupling member 35 of the upper sleeve portion 30A of anadjacent link 28. Likewise, a coupling member 35 of the lower sleeveportion 30B of one link 28 is attached to a corresponding couplingmember 35 of the lower sleeve portion 30B of an adjacent link 28. Thecoupling members 35 can be flexible or rigid, and can be integrallyformed with, or discreetly connected to, the corresponding legs 33. Thelinkage 26 can include any number of links 28 as desired, such that theupper sleeve portions 30A of each link 28 are connected, and the lowersleeve portions 30B of each link 28 are connected.

Referring now to FIGS. 2A and 5, the cross beam 31 of each outer sleeveportion 30A and 30B defines an outer vertebral engagement surface 32 asdescribed above, and further defines an opposing transverse innerengagement surface 40 that extends laterally between the opposingtransverse legs 33. The inner engagement surface 40 is sloped verticallyso as to define an angle θ with respect to a longitudinal axis L-L thatcan be between 0° and 90°, for instance between about 10° and about 50°,such that the engagement surface 40 of each outer sleeve portion slopestransversely in along a longitudinal direction from the rear end 29toward the front end 27 of the linkage 26. Thus, the inner engagementsurface 40 of the upper sleeve portion 30A slopes vertically down alonga longitudinal direction from the rear end 29 toward the front end 27,and the inner engagement surface 40 of the lower sleeve portion 30Bslopes vertically up along a longitudinal direction from the rear end 29toward the front end 27.

The engagement surfaces 40 of the upper sleeve portions 30A can definean angle greater θ or less than that of the engagement surfaces 40 ofthe lower sleeve portions 30B, thereby causing the upper sleeve portion30A to expand at a higher or lower expansion rate, respectively,relative to the lower sleeve portion 30B. In this regard, it should beappreciated that the angle θ of one of the inner engagement surfaces 40relative to the longitudinal axis L-L could be zero, while the angle θof the other engagement surface 40 relative to the longitudinal axis L-Lis non-zero, thereby causing only the outer sleeve portion of the otherengagement surface to expand during operation.

The inner engagement surfaces 40 of each link 28 can be aligned with,and extend parallel to, the engagement surfaces 40 of the other links 28of the linkage 26. Thus, the outer sleeve 30 of each link 28 can extendtransversely a distance at its front end greater than at its rear end.Each link 28 can further include an engagement member as one or moreprojections or that extends transversely in from the engagement surfaces40. The projections can be in the form of ridges, teeth, or likestructure that is configured to mate with a complementary structure tofixes the implant in an expanded position. In the illustratedembodiment, the projections are shown as reverse angled teeth 44 thatproject transversely in from the engagement surface 40. Thus, for thepurposes of description, the engagement member, or one or moreprojections, is referred to herein as teeth.

The teeth 44 project down from the engagement surface 40 of the uppersleeve portion 30A, and teeth project up from the engagement surface 40of the lower sleeve portion 30B. The teeth 44 can define a root end 45that is substantially in-line with the corresponding engagement surfaces40, and triangular tips 46 that are transversely offset from theengagement surface. Adjacent tips 46 can be spaced apart any desireddistance, such as between about 0.5 mm and about 5 mm. The teeth 44 ofeach link 28 can be substantially identically sized and shaped, suchthat a line connecting the tips 46 of adjacent teeth 40 extends parallelto the engagement surface 40. The outer sleeve portions 30A and 30Bfurther define pockets 43 disposed between and defined by adjacent teeth44. The pockets 43 thus have a size and shape substantially identical tothe adjacent teeth 44 that define the pockets 43.

Each link 28 defines an internal void 38 that extends transverselybetween opposing cross beams 31 and laterally between opposing legs 33of each outer sleeve portion 30A and 30B. The linkage 26 includes aninner core 50 that is disposed within the internal void 38 of each link28, and is retained by the outer sleeve portions 30A and 30B. The innercore 50 can abut the transverse inner surfaces 40 of the cross beams 31such that, during operation, longitudinal movement of the inner core 50relative to the outer sleeve 30 causes the outer sleeve 30 to expand ina first direction, such as the vertical direction (see FIG. 7) andalternatively or additionally a second direction perpendicular to thetransverse or vertical direction, such as the horizontal direction (seeFIGS. 15A-C).

In the embodiment illustrated in FIGS. 2A-2B, the inner core 50 includesa core body 52 that defines opposing lateral surfaces that can face orabut the legs 33 of the outer sleeve, and opposing transverse outer, orupper and lower, engagement surfaces 54. The portion of the inner core50 disposed within one of the links 28 can be integrally connected oralternatively fastened to the portions of the inner core 50 that aredisposed in the other links 28 of the linkage 26 using any suitablemechanical or adhesive fastening member.

When the inner core 50 is installed in the internal void 38 of the outersleeve 30, the engagement surfaces 54 can mate with, or abut, thecorresponding sloped engagement surfaces 40 of the outer sleeve portions30A and 30B. The engagement surfaces 54 are thus transversely slopedwith respect to the longitudinal axis L-L, and thus extend parallel tothe corresponding engagement surfaces 40. The inner core 50 can furtherinclude an engagement member as one or more projections that extendtransversely out from the engagement surfaces 54. The projections can bein the form of ridges, teeth, or like structure that is configured tomate with a complementary structure to fix the implant in an expandedposition. In the illustrated embodiment, the projections are shown asreverse angled teeth 56 that project transversely out from theengagement surfaces 54. Thus, for the purposes of description, theengagement member, or one or more projections, is referred to herein asteeth 56.

The teeth 56 can be sized and shaped substantially identical withrespect to teeth 44, so as to mate with teeth 44. The teeth 56 define aroot end that is substantially in-line with the corresponding engagementsurfaces 54, and triangular tips 60 that are transversely offset fromthe engagement surface. The teeth 56 are identically sized and shaped,such that a line connecting the tips 60 of adjacent teeth 56 extendsparallel to the engagement surface 54. Thus, the teeth of the inner core50 become transversely inwardly disposed along a direction from the rearof the link 28 toward the front of the link 28. The inner core body 52further defines pockets 57 disposed between and defined by adjacentteeth 56. The pockets 57 thus have a size and shape substantiallyidentical to the adjacent teeth 56 that define the pockets 57.

With continuing reference to FIG. 2B, the teeth 44 are sized and shapedto interlock with mating teeth 56, and reside in the pockets 57 definedbetween adjacent teeth 56. Likewise, the teeth 56 are sized and shapedto interlock with mating teeth 44, and reside in the pockets 43 definedbetween adjacent teeth 44. The teeth 44 and 56 can define a sawtoothshape that is undercut such that the tips 46 and 60 of interlockingteeth 44 and 56 overlap each other a distance D, which can be greaterthan 0 mm and less than or equal to 2 mm. Accordingly, a transversecompressive force applied to the link 28 causes the teeth 44 and 56 tocam along each other to an interlocked position, such that interferencebetween the tip ends 46 and 60 resists vertical separation of the outersleeve 30 from the inner core 50 during insertion of the implant 20 intothe intervertebral space. Moreover, as the implant 20 is inserted intothe disc space 22, the bodily tissue will apply a forward longitudinalforce against the outer sleeve 30, thereby biasing the teeth 44 and 56into their interlocked position, whereby motion of the core 50 relativeto the outer sleeve 30 is permitted in the longitudinally forwarddirection, but prevented in a longitudinally rearward direction.

The opposing tips 46 and 60 of interlocking teeth 44 and 56 can bespaced a transverse distance so as to define a height H that can bewithin a range between 0 mm and about 3 mm. The teeth 44 and 56 canfurther define an angle θ₂ between about 10° and about 50° with respectto the longitudinal axis L-L.

Referring now to FIG. 6, the linkage 26 can be coupled to an insertiontool 70, which includes a biasing member 64, an inner holding sleeve 72,and an outer holding sleeve 74. The biasing member 64 is operable tomove the inner core member 50 longitudinally forward relative to theouter sleeve 30. In the illustrated embodiment, the inner core body 52defines an internal longitudinally elongate bore 62 that is sized andshaped to receive the biasing member 64, which can be provided as alongitudinally extending rod or wire 66 connected to a transversestopper 68 at one longitudinal end of the wire 66. The wire 64 can bemade from vitalium, titanium, or the like. The stopper 68 is sized andshaped to abut the rear surface of the inner core 50, but not the outersleeve, of the rearmost link 28, and the wire 66 can extend through thebore 62 of all inner core bodies 52 along the linkage 26, and projectforward from the front end 27 of the linkage. The wire 66 can be held inplace inside the bore 62 by an interference fit or any suitable fixationmechanism.

The inner annular holding sleeve 72 surrounds the wire 66 at a locationforward from the front end 27 of the linkage 26, and can guide the wire66 during operation. The wire 66 can be pulled in a longitudinal forwarddirection relative to the inner holding sleeve 72 such that the innerholding sleeve 72 abuts the front end of the core body 52 of thefront-most link. The engagement of the inner holding sleeve 72 and thecore body 52 allows a user to maintain control of the position of theimplant 20 during insertion into the intervertebral space 22 as tensionis applied to the wire 66.

The outer annular holding sleeve 74 is configured to abut the front endof the forwardmost outer sleeve 30 at a location that is out oftransverse alignment with the core body 52. The outer holding sleeve 74provides reciprocal biasing member that is operable to provide a biasingforce that is equal and opposite to the force applied from the biasingmember 64 to the core 50. In this regard, the outer holding sleeve 74can be referred to as a brace member.

Accordingly, as a first force F₁ is applied to the wire 66 along alongitudinally forward direction, the stopper 68 applies a correspondinglongitudinally forward biasing force to the rear link 28. The outerholding sleeve 74 applies a force F₂ into the outer linkage sleeve 30that is equal and opposite with respect to the force F₁. The force F₁applied to the wire 62 thus causes the inner core 50 to translatelongitudinally forward with respect to the outer sleeve 30.

Referring also to FIG. 7, as the inner core 50 translates forward withrespect to the outer sleeve 30, the engagement surfaces 40 ride alongthe complementary engagement surfaces 54, thereby causing the outersleeve portions 30A and 30B to deflect vertically away from each other.As the outer sleeve portions 30A and 30B deflect away from each other,the intervertebral implant 20 expands in the transverse, or vertical,direction. The slope of the upper and lower mating engagement surfaces40 and 54 determines the rate at which the upper and lower sleeves 30Aand 30B expand, respectively.

As the inner core 50 moves in the forward direction with respect to theouter sleeve 30, the tips 46 and 60 of the engagement members, or teeth44 and 56, cam over each other, thus causing the height of the implant20 to increase in increments substantially equal to the height H of theteeth 44 and 56. Once a desired height is achieved and the biasing forceis removed from the wire 62, the engaging teeth 44 and 56 can allowslight relative motion of the outer linkage sleeve 30 relative to theinner core 50 in the longitudinally forward direction, which can causethe outer teeth 34 of the sleeve to scuff the inner surfaces of theadjacent vertebrae 24, thereby facilitating fusion of the sleeveportions 30A and 30B to the vertebrae 24.

Once the teeth 44 and 56 become interlocked, relative motion between theinner core 50 and the outer sleeve 30 is prevented in the absence of theapplication of another biasing force to the cable 66. It should thus beappreciated that the linear forward motion of the inner core 50 relativeto the outer sleeve 30 causes the intervertebral implant 20, or outersleeve portions 30A and 30B, to expand from an initial, or relaxedposition having a first height, to a second or an expanded positionhaving a second height that is greater than the first height. The teeth44 and 56 provide engagement members that prevent the outer sleeveportions 30A and 30B from contracting toward each other once theintervertebral implant 20, sleeve outer portions 30A and 30B, havereached the desired expanded position. It should be appreciated thatwhile the engagement surfaces 40 and 54 of each link 28 each include aplurality of corresponding teeth, each engagement surfaces 40 and 54could alternatively comprise one or more teeth.

During operation, the implant 20 is inserted into the intervertebralspace 22 in the initial position, and subsequently expanded to a secondexpanded position so as to abut and position the adjacent vertebrae 24to a desired vertical position that causes the intervertebral space toachieve a desired height. The intervertebral implant 20 can thus bereferred to as an intervertebral spacer that causes the intervertebralspace 22 between adjacent vertebrae to increase to a desiredcaudocranial height. An autograft or bone substitute can be placedaround the implant 20 in the intervertebral space 22 if desired.

It should be appreciated that, as shown in FIG. 6, the core body 52 ofthe rear link 28 can be sized having a longitudinal length that issubstantially longer than that of the corresponding outer sleeve 30. Asa result, the core 50 can project rearward with respect to the sleeve 30of the rearmost link 28 by an offset distance “O” when the implant 20 isin the initial or relaxed position. The offset distance O can bepreselected based, for instance, on the slope of the engagement surfaces44 and 54 and the desired expansion of the outer sleeve 30, such thatonce the implant 20 has reached the desired final height, the rearsurface of the core 50 can be substantially flush with the rear surfaceof the outer sleeve 30 the rear link 28, as shown in FIG. 7.

Moreover, FIG. 6 shows the front end of the core body 52 of the frontlinkage 28 as being substantially flush with the front end of the outersleeve 30 of the front linkage 28 when the implant 20 is in the initialposition. Accordingly, as shown in FIG. 7, when the implant is in theexpanded position, the front end of the core body 52 of the frontlinkage 28 extends forward from the front end of the outer sleeve 30 ofthe front linkage 28. It should be appreciated, however, that the frontend of the core body 52 of the front linkage 28 could alternatively berecessed with respect to the front end of the outer sleeve 30 of thefront linkage 28 a distance equal to the offset distance O when theimplant 20 is in the initial position. Accordingly, when the implant 20is in the expanded position, the front end of the core body 52 of thefront linkage 28 could be substantially flush with the front end of theouter sleeve 30 of the front linkage 28.

Referring now to FIGS. 8A-C, the expandable intervertebral implant 20can include a retainer member in the form of one or more, such as aplurality of, bands 84 that are configured to apply a compressiveretention force against the links 28 that can assist in maintaining thestructural integrity of the implant 20 as the implant 20 is insertedinto the intervertebral space 22 and expanded to the vertically expandedposition. In particular, the linkage 26 can include laterally opposingtransverse slots 82 that extend vertically through the coupling members35. The coupling members 35 can include a lateral portion that extendsin a laterally extending groove 86 disposed between adjacent links 28.

A metallic or elasticized band 84 can be inserted through the laterallyopposing slots 82 and sit in the grooves 86 such that the band 84surrounds the legs 33 of the outer sleeve portions 30A and 30B. The band84 can include terminal ends 85A and 85B that form an interlockingtongue-and-groove. Thus, the terminal ends 85A and 85B can be clippedtogether, and the terminal ends can be placed inside one of the slots 82so as to reduce the possibility that the band 84 would be inadvertentlyseparated. The bands 84 can apply a compressive force that biases theouter sleeve portions 30A and 30B against each other and against theinner core 50, thereby assisting in the retention of the teeth 44 and 56in their interlocked configuration. The bands 84 can be radiolucent soas to provide an indication of the position and angular orientation ofthe implant 20 during the implantation procedure.

Referring now to FIG. 9A-B, the expandable intervertebral implant 20 caninclude a retainer member constructed in accordance with an alternativeembodiment. In particular, the legs 33 do not define a transverse slotextending vertically therethrough. Instead, an elasticized band 88 canbe stretched over one or more of the links 82 and inserted into thegroove 86. The elasticity of the band 88 can apply a compressive forcethat biases the outer sleeve portions 30A and 30B against each other andagainst the inner core 50, thereby assisting in the retention of theteeth 44 and 56 in their interlocked configuration. The plurality ofbands 88 can be radiolucent so as to provide an indication of theposition and angular orientation of the implant 20 during theimplantation procedure.

Referring now to FIG. 10, the expandable intervertebral implant can beconstructed such that the vertebral engagement surfaces 32 define alordotic profile when the implant 20 is in the expanded position. Inaccordance with the illustrated embodiment, the slope S of theengagement surfaces 40 and 54 relative to the longitudinal axis L-L ofeach link 28 vary from link to link. Thus, the opposing engagementsurfaces 40 and 54 of one link are angled, or not parallel, with respectto the corresponding opposing engagement surfaces 40 and 54 of anadjacent link. For instance, the slope of each interfacing engagementsurfaces 40 and 50 of each link 28 relative to the longitudinal axis L-Lhas a magnitude that decreases along a direction from the rear link 28toward the front link 28. Thus, the magnitude of the slope of thecomplementary engagement surfaces 40 and 54 of a given link 28 isgreater than that of forwardly disposed links 28, and less than that ofrearwardly disposed links 28.

Accordingly, as the implant 20 expands, the outer sleeve portions 30Aand 30B of each link 28 will become vertically displaced at differentrates. In the illustrated embodiment, the rate of outer sleeve verticaldisplacement will decrease in a direction from the rear link 28 towardthe front link 28. It should, of course, be appreciated that the slopeof the engagement surfaces 40 and 50 of each link could alternativelydecrease in a direction from the front link 28 toward the rear link 28such that the rate of vertical displacement would decrease in adirection from the front link 28 toward the rear link 28. Alternativelystill, the middle links 28 can expand at a rate that is greater than orless than the forward and rearward spaced links 28.

In the embodiment illustrated in FIG. 10, the vertebral engagementsurfaces 32 of the opposing outer sleeve portions 30A and 30B can besubstantially flat in the longitudinal direction. The slope of opposingvertebral engagement surfaces 32 of each link 28 can vary from link tolink. Thus, the vertebral engagement surfaces 32 of one link are angled,or not parallel, with respect to the engagement surfaces 32 of anadjacent link. It can also be said that the engagement surfaces 32 ofeach link 28 are sloped at an angle with respect to the longitudinaldirection that is different than the angle at which the engagementsurfaces 32 of the other links are sloped relative to the longitudinaldirection.

The opposing engagement surfaces 32 of the outer sleeve portions 30A and30B of a given link 28 can be equal and opposite relative to thelongitudinal axis L-L. As illustrated, the vertebral engagement surfaces32 of the links 28 each define a slope having a magnitude with respectto the longitudinal axis L-L that decrease from link to link as theslope of the corresponding engagement surfaces 40 and 50 increase whenthe implant 20 is in the initial position. Thus, in the illustratedembodiment, the slope of each of the vertebral engagement surfaces 32 ofthe links 28 has a magnitude that decrease in direction from the frontend 27 of the linkage 26 toward the rear end 29 of the linkage. Themagnitude of the slope of the opposing vertebral engagement surface 32of a given link 28 is greater than that of rearwardly disposed links 28,and less than that of forwardly disposed links. Alternatively, the slopeof the opposing vertebral engagement surfaces 32 of each link 28 couldbe substantially identical from link to link.

Referring now to FIG. 11, when the inner core 50 is moved longitudinallyforward relative to the outer sleeve 30 to move the implant from theinitial position to the expanded position in the manner described above,the links 28 expand at different rates. In particular, a given link 28expands at a faster rate than forwardly disposed links, and at a rateslower than rearwardly disposed links. As a result, when theintervertebral implant 20 is in the expanded position illustrated inFIG. 11, the opposing outer sleeve portions 30A and 30B of each link 28have expanded a distance that is greater than those of forwardlydisposed links, and less than those of rearwardly disposed links. Thus,the implant 20 defines vertebral engagement surfaces 32 that are slopedtransversely outward with respect to the longitudinal axis L-L in adirection from the front end 27 toward the rear end 29. Moreover, thevertebral engagement surfaces 32 of each outer sleeve portion 30A and30B are in line with the vertebral engagement surfaces 32 of the otherlinks 28 of the linkage 26, thereby creating reliable engagementsurfaces with the vertebrae 24.

Referring to FIGS. 12A-B, it should be appreciated that the links 28 canbe coupled so as to permit relative vertical motion between adjacentlinks. Accordingly, the adjacent links 28 can be coupled by a joint,such as a tongue-and-groove joint 90. The joint 90 includes a pair offirst laterally opposing engagement members 92 attached to one of theadjacent links 28. The engagement members 92 extend vertically, and eachincludes a beveled surface 94 that slopes laterally inward along adirection longitudinally away from the link 28. The other of theadjacent links 28 includes a second laterally elongate engagement member96 that extends laterally between the opposing engagement members 92.The engagement member extends vertically, and includes laterallyopposing beveled surfaces 98 that slopes laterally outward along adirection longitudinally away from the link 28. The beveled surfaces 94and 98 engage each other to interlock the adjacent links with respect tolongitudinal separation, while allowing for relative vertical motionalong the beveled surfaces 94 and 98, and thus relative vertical motionbetween the adjacent links 28. A retainer member, such as band 88, canfurther be inserted into one or more of the grooves 86 that separate theadjacent links 28 so as to further maintain the structural integrity ofthe linkage 26 during use in the manner described above.

Alternatively or additionally, the expandable intervertebral implant 20can include an auxiliary retainer such as a flexible band 100 asillustrated in FIG. 13. The band 100 defines a body 101 that extendsgenerally in the longitudinal direction, and defines a pair of opposingterminal ends 102 that each define connection locations that can beconnected to an outer sleeve portion 30A or 30B of a different one ofthe plurality of links 28. The terminal ends 102 can define a hingedconnection with respect to the outer sleeve portion, or can define afixed connection such that the flexibility of the band 100 allows theterminal ends 102 and other connection locations to rotate relative tothe body 101. The bands 100 can be fastened to the outer sleeve portions30A and 30B using any suitable mechanical fastener.

In the illustrated embodiment, the terminal ends 102 of one band 100 areconnected to the laterally outer surfaces of the upper sleeve portions30A of the longitudinally outermost links 28. The terminal ends 102 ofanother band 100 are connected to the laterally outer surfaces of thelower sleeve portions 30B of the longitudinally outermost links 28. Apair of substantially identical bands can be connected to the opposingouter lateral surfaces of the upper and lower sleeve portions 30A and30B. Thus, the bands 100 provide a longitudinal compressive force to alllinks 28 disposed between the terminal band ends 102. Alternatively, thebands 100 can be connected to one or more, up to all, links 28 that aredisposed between the terminal ends 102 of the bands 100.

It should be appreciated that FIGS. 10-13 illustrate the intervertebralimplant 20 configured to produce a lordotic profile in accordance withone embodiment, and that alternative embodiments can be provided tocreate a lordotic profile. For instance, referring to FIG. 13, thevertebral engagement surfaces 32 of each outer sleeve portions 30A and30B are aligned with the vertebral engagement surfaces 32 of thecorresponding outer sleeve portions 30A and 30B of the adjacent links.Thus, the vertebral engagement surfaces 32 of each outer sleeve portion30A are aligned and parallel to each other, and the vertebral engagementsurfaces 32 of each outer sleeve portion 30 b are aligned and parallelto each other. Moreover, the engagement surfaces 32 of each outer sleeveportion 30A and 30B can be sloped with respect to the longitudinal axisL-L. In the illustrated embodiment, the engagement surfaces 32 define aslope S₁ that is angled transversely out from the longitudinal axis L-Lin a direction from the front end 27 of the linkage 26 toward the rearend of the linkage. It should be appreciated, however, that theengagement surfaces 32 could alternatively slope transversely in fromthe longitudinal axis L-L in a direction from the front end 27 of thelinkage 26 toward the rear end of the linkage.

Furthermore, the engagement surfaces 40 and 50 of each outer sleeveportion 30A are aligned with and extend parallel to the engagementsurfaces 40 and 50 of the outer sleeve portions 30A of the other links28. Likewise, the engagement surfaces 40 and 50 of each outer sleeveportion 30B are aligned with and extend parallel to the engagementsurfaces 40 and 50 of the outer sleeve portions 30B of the other links28. Accordingly, as the implant is expanded to the expanded positionillustrated in FIG. 13, each link 28 is displaced transversely outwardat the same displacement rate of the other links, and the vertebralengaging surfaces 32 maintain the lordotic profile described above.

Thus, the expandable intervertebral implant 20 is configured to expandalong the transverse direction and can be further configured such thatthe vertebral engaging surfaces 32 can define a lordotic profile whenengaged with the vertebrae. Alternatively or additionally, theintervertebral implant 20 can be configured such that the vertebralengaging surfaces 32 of the links 28 combine to define a nonlinearshape, such as a curved convex shape having outer longitudinal ends thatare disposed transversely inward with respect to a longitudinal middleportion.

Referring to FIG. 15A, the opposing axially inner surfaces of the legs33 of each outer sleeve portion 30A and 30B can define laterallyopposing, and vertically extending, engagement surfaces 110 that can belongitudinally elongate, and sloped laterally with respect to thelongitudinal axis L-L at any desired angle as described above withrespect to the transverse angle formed between inner engagement surface40 and the longitudinal axis. Accordingly, that the engagement surface110 of each sleeve portion slopes laterally out from the longitudinalaxis along a direction from the front end 27 toward the rear end 29 ofthe linkage 26. In this regard, it should be appreciated that thelaterally sloped engagement surface 110 can be constructed as describedabove with respect to the transversely sloped engagement surface 40.However, the cross beam 31 of each outer annular sleeve is discontinuousalong the lateral direction, such that each leg the outer sleeveportions 30A and 30B is free to move relative to the other leg of sameouter sleeve portion in the lateral direction. Each leg of a given outersleeve portion is free to move in the transverse direction with respectto the legs of the opposing outer sleeve portion in the manner describedabove.

The engagement surfaces 110 of the upper sleeve portions 30A can definean angle greater or less than that of the other, and can further definean angle greater or less than that of the engagement surfaces 110 of thelower sleeve portions 30B, thereby causing one lateral side of the outersleeve 30 to expand laterally at a higher or lower expansion rate,respectively, relative to the other lateral side of the outer sleeve 30.In this regard, it should be appreciated that the angle of one or bothof the of the inner engagement surfaces 110 relative to the longitudinalaxis L-L could be zero, while the angle of the other engagement surface110 relative to the longitudinal axis L-L is non-zero, thereby causingonly one lateral side of the outer sleeve to expand laterally duringoperation.

The engagement surfaces 110 of each link 28 can be aligned with, andextend parallel to, the engagement surfaces 110 of the other links 28 ofthe linkage 26. Thus, the outer sleeve 30 of each link 28 can extendlaterally at its front end a greater amount than at its rear end. Eachlink 28 can further include an engagement member in the form of reverseangled teeth 114 that project laterally inward from the engagementsurface 110. The lateral teeth 114 can be constructed in the mannerdescribed above with reference to the transverse teeth 44.

The inner core body 52 defines laterally outer engagement surfaces 124that are configured to engage the engagement surfaces 110 of the upperand lower sleeves 30A and 30B. The inner core body 52 can extendvertically a sufficient distance such that each engagement surface 124can engage with the pair of complementary engagement surfaces 110 oneach lateral side of the sleeve 30. The engagement surfaces 124 can belaterally sloped with respect to the longitudinal axis L-L, and can thusextend parallel to the corresponding engagement surfaces 110. Thelateral engagement surfaces 124 can be constructed as described abovewith respect to the transverse engagement surfaces 54. The inner core 50can further include an engagement member in the form of reverse angledteeth 126 that project laterally out from the engagement surfaces 124.The teeth 126 can be sized and shaped substantially identical withrespect to teeth 114, so as to mate with teeth 114. The teeth 126 can beconstructed in the manner described above with respect to teeth 56.

As illustrated in FIG. 15B, the outer sleeve portions 30A and 30B can beretained by a retainer such as a plurality of bands 84 in the mannerdescribed above. Slots 82 can extend vertically through both pairs ofopposing laterally outer legs 33, and the band 84 can be inserted intothe slots 82 and placed in the groove 86 in the manner described aboveto apply compressive retention forces onto the linkage, therebyassisting in securing the structural integrity of the expandableintervertebral implant 20. Alternatively, as illustrated in FIG. 15D,the retainer may be provided as an elasticized band 88 that is placed inthe groove 86 in the manner described above to apply laterally andtransverse compressive securing forces.

Referring now to FIGS. 15A and 15C, as the inner core 50 moves in theforward direction with respect to the outer sleeve 30, the engagementsurfaces 40 ride along the complementary engagement surfaces 54, and theteeth 44 and 56 cam over each other, thereby causing the outer sleeveportions 30A and 30B to incrementally deflect vertically away from eachother in the manner described above. Furthermore, the engagementsurfaces 110 ride along the complementary engagement surfaces 124, andthe teeth 114 and 126 cam over each other, thereby causing the laterallyouter portions of the outer sleeve 30 to incrementally deflect laterallyaway from each other from a first laterally contracted position to asecond laterally expanded position. It should be appreciated that theengagement surfaces 110 and 124 can have a slope that is greater than orless than the slope of engagement surfaces 40 and 54, such that theimplant 20 can expand vertically at a greater rate or a lesser rate thanthe implant 20 expands laterally.

It should be appreciated that a kit can be provided that includes all ora portion of the expandable intervertebral implant 20 constructed inaccordance with any of the embodiments described herein. For example,the kit can include one or more of the components of the expandableintervertebral implant, such as the upper and lower outer sleeveportions 30A and 30B, the inner core 50, bands 84 and 88, and aplurality of links 28. The one or more components included in variouskits can have one or more varying characteristic such as size and/orshape. For instance, a first kit can be provided having one or morecomponents, for instance outer sleeve portions 30A and 30B, the innercore 50, bands 84 and 88, and a plurality of links 28, that have adifferent size or shape to accommodate different expansion rates,different longitudinal and/or lateral lengths, and different directionsof expansion, for instance transverse expansion alone or coupled withlateral expansion. Some components in a given kit may permit the implant20 to produce a lordotic profile in the manner described above, whileother components in the kit may permit the implant to produce ahorizontal upper and lower vertebrae-engaging surface. The kit canfurther include components of the insertion tool 70 as will now bedescribed.

In particular, referring now to FIGS. 16A-C, the insertion tool 70 canbe configured to engage the intervertebral implant 20 such that theimplant 20 may be inserted into the intervertebral space 22 andsubsequently expanded in the manner described above. Once theintervertebral implant is disposed in the intervertebral space, theinsertion tool can include biasing members that apply a biasing force tothe implant, thereby causing the implant to expand in any manner asdescribed above. Once the implant 20 has reached the desired expansionposition, the insertion tool 70 may be disengaged from the implant 20.

The insertion tool 70 can include the inner annular holding sleeve 72,the biasing member 64 that extends inside the inner annular holdingsleeve 72, and the outer annular holding sleeve 74 that receives theinner annular holding sleeve 72. Once the holding member 70 is moved toposition such that the inner annular holding sleeve 72 abuts the innercore 50 and the outer annular holding sleeve 74 abuts the outer sleeve30, a force F1 can be applied to the wire 66 that causes the implant toexpand in the manner described above.

Referring to FIGS. 17A-C, the inner annular holding sleeve 72 caninclude a longitudinally elongate body 151 having a threaded engagementsurface 152 at a distal end that is configured to be threadedly receivedin the outer annular holding sleeve 74. The inner annular holding sleeve72 can include a proximal end having a forked abutment member 154. Theforked abutment member 154 can include a pair of spaced prongs 156 thatare configured to abut the inner core 50 in the manner described above.The wire 62 can thus extend through the inner core 50 of each link 28,between the prongs 156 and through the inner annular holding sleeve 72.The free end of the wire that extends through the inner annular holdingsleeve can be coupled to any suitable tensioning device configured toapply a biasing force sufficient to cause the intervertebral implant 20to expand.

Referring now to FIGS. 18A-B, the insertion tool 70 can further includean angulated member 158 that is connected between the forward end 127 ofthe linkage 26, and the proximal ends of the inner and outer holdingsleeves 72 and 74. The angulated member 158 can include a rectangularblock 159, a cylindrical body 160 rigidly attached to the block 159, anda bore 162 extending through the body 160 sized to receive the wire 66.The wire 66 can thus extend through the linkage 56, the cylindrical body160, and the inner sleeve 72. The outer sleeve 73 can define a bore 164extending longitudinally therethrough, and a directional rod 166extending through the bore 164. The directional rod 166 defines aproximal end that is pivotally coupled to the block 159 at a connectionlocation 158 that is laterally offset with respect to the lateral centerof the cylindrical body 160.

During operation, the rectangular block 159 abuts the inner core 50, andthe directional rod 166 can be moved longitudinally forward andrearward, thereby causing the cylindrical body 160 to rotate relative tothe proximal ends of the inner and outer sleeves 72 and 74. As thecylindrical body 160 rotates, the rectangular block 159 causes theintervertebral implant to change its angular orientation in thehorizontal plane defined by the lateral and longitudinal directions. Asillustrated, movement of the rod 166 in a forward direction causes theintervertebral implant 20 to pivot in a clockwise direction, whilemovement of the rod 166 in a rearward direction causes the implant topivot in a counterclockwise direction. It should be appreciated, ofcourse, that the rod 166 could alternatively be connected to therectangular block 159 at a location that causes the intervertebralimplant 20 to pivot in the clockwise direction when the rod is movedrearward, and counterclockwise when the rod is moved forward.

During operation, the longitudinal position of the rod 166 can bedetermined prior to inserting the intervertebral implant 20 into thedisc space 22 so as to define an angular orientation of the implant 20relative to the inner and outer sleeves 72 and 74. The angularorientation of the implant 20 allows the implant to be inserted into thebody cavity along an anteroposterior directional approach or aposterior-anterior directional approach, while at the same timeorienting the implant such that the longitudinal axis L defines adesired angle with respect to the anterior and posterior directions whenthe implant is inserted into the disc space 22. Once the intervertebralimplant 20 has been inserted into the disc space 22, the wire 66 can bemoved longitudinally forward to cause the implant 20 to expand in thetransverse direction T alone, or in the transverse direction T andsimultaneously the lateral direction A. Moreover, as the implant 20expands in either the transverse direction T alone or in the transversedirection T simultaneously with the lateral direction A, the opposingtransverse vertebral-engaging surfaces 32 can remain flat and parallelwith each other, or can define an angular orientation configured torestore lordosis to the vertebrae 24 in the manner described above.

Finally, referring to FIGS. 19A and 19B, once the implant 20 has beenpositioned in the intervertebral space 22 and expanded to the desiredexpanded position, the outer sleeve 72 can be removed out of engagementwith the intervertebral implant, and the remaining portions of the tool70 can be removed by cutting the portion of the intervertebral body 50that protrudes from the front end 127 of the linkage 26 along a cut line168 along the lateral-transverse plane LT. The cut can be made in fromopposing directions, for instance using reciprocal blades at opposinglocations, such that the blades can cut through the inner core body 52and the wire 66 and cause the body 50 to crimp around the wire 66.Alternatively, the inner core body 52 can be cut in any desired manner,and a separate crimping tool can be used to crimp the body 50 around thewire 66 after the body 50 and wire 66 have been cut, thereby securingthe wire and preventing the wire 66 from being inadvertently removedafter the surgical procedure has been completed.

The embodiments described in connection with the illustrated embodimentshave been presented by way of illustration, and the present invention istherefore not intended to be limited to the disclosed embodiments.Furthermore, the structure and features of each the embodimentsdescribed above can be applied to the other embodiments describedherein. Accordingly, those skilled in the art will realize that theinvention is intended to encompass all modifications and alternativearrangements included within the spirit and scope of the invention, asset forth by the appended claims.

What is claimed:
 1. An expandable intervertebral implant that isinsertable into an intervertebral disc space and expandable from aninitial position to an expanded position, the expandable intervertebralimplant comprising: a first outer portion defining opposed ends spacedfrom each other along a longitudinal direction, the first outer portionfurther defining a first bone contacting surface, wherein thelongitudinal direction includes a first direction and a second directionopposite the first direction; a second outer portion defining opposedends spaced from each other along the longitudinal direction, the secondouter portion further defining a second bone contacting surface spacedfrom the first bone contacting surface along a transverse direction thatis substantially perpendicular to the longitudinal direction, wherein atleast one of the first and second outer portions further defines firstand second engagement surfaces that are spaced from each other along thelongitudinal direction, and the second bone contacting surface definesan orientation relative to the first bone contacting surface; and aninner core disposed between the first and second outer portions, theinner core defining third and fourth engagement surfaces that are spacedfrom each other and aligned with each other along the longitudinaldirection, wherein (i) translation of the inner core in the firstdirection relative to the at least one of the first and second outerportions causes the third and fourth engagement surfaces to translatewith each other and in the first direction ride along the first andsecond engagement surfaces, respectively, thereby causing the at leastone of the first and second outer portions to deflect away from theother of the first and second outer portions along the transversedirection from the initial position to the expanded position, (ii) therelative orientation of the second bone contacting surface with respectto the first bone contacting surface remains constant before, during,and after deflection of the at least one of the first and second outerportions away from the other of the first and second outer portionsalong the transverse direction, (iii) the implant defines a height fromthe first bone contacting surface to the second bone contacting surfacealong the transverse direction, and the expandable intervertebralimplant is designed such that when the expandable intervertebral implantis in the initial position, the height is a minimum height such that theimplant is unable to achieve a height less than the minimum height viamovement of the inner core relative to each of the first and secondouter portions along the longitudinal direction, and (iv) when theexpandable intervertebral implant is in the expanded position, the firstand second outer portions are prevented from moving toward each other ina direction from the expanded position to the initial position while (a)the first engagement surface is in abutment with the third engagementsurface and (b) the second engagement surface is in abutment with thefourth engagement surface.
 2. The expandable intervertebral implant ofclaim 1, wherein each of the first and second outer portions is movablealong the transverse direction with respect to the other of the firstand second outer portions as the expandable intervertebral implantexpands from the initial position to the expanded position.
 3. Theexpandable intervertebral implant of claim 1, wherein each of the firstand second outer portions further defines respective first and secondengagement surfaces that are spaced from each other along thelongitudinal direction, and the inner core includes first and secondpairs of third and fourth engagement surfaces, such that (i) the thirdand fourth engagement surfaces of the first pair are configured to abutthe first and second engagement surfaces, respectively, of the firstouter portion as the inner core translates in the first directionrelative to the first and second outer portions, and (ii) the third andfourth engagement surfaces of the second pair are configured to abut thefirst and second engagement surfaces, respectively, of the second outerportion as the inner core translates in the first direction relative tothe first and second outer portions.
 4. The expandable intervertebralimplant of claim 1, wherein each of the first, second, third and fourthengagement surfaces are sloped with respect to the longitudinaldirection and are substantially parallel to each other.
 5. Theexpandable intervertebral implant of claim 1, further comprising a firstmember configured to abut the inner core and apply a biasing force tothe inner core that drives the inner core to translate in the firstdirection relative to the at least one of the first and second outerportions.
 6. The expandable intervertebral implant of claim 5, whereinthe inner core defines a bore, and the expandable intervertebral implantfurther comprises an elongate member that extends from the first memberand is received in the bore, and is configured to apply a biasing forcein the first direction that drives the inner core to translate relativeto the at least one of the first and second outer portions along thelongitudinal direction.
 7. The expandable intervertebral implant ofclaim 6, wherein the elongate member is received in the bore at a firstlongitudinal end of the inner core, and extends away from the inner coreat a second longitudinal end of the inner core that is opposite thefirst longitudinal end along the longitudinal direction.
 8. Theexpandable intervertebral implant of claim 7, wherein the elongatemember defines a portion that is aligned with each of the first andsecond outer portions along the transverse direction prior totranslation of the inner core in the first direction, and the portion ofthe elongate member is offset from the first and second outer portionsalong the longitudinal direction after the inner core has translatedalong the longitudinal direction.
 9. The expandable intervertebralimplant of claim 8, wherein the elongate member is translatably coupledto the inner core such that the elongate member and the inner coretranslate together in the first direction as the expandable implantmoves from the initial position to the expanded position.
 10. Theexpandable intervertebral implant of claim 6, further comprising acylindrical body that defines an articulation surface that is configuredto receive the elongate member.
 11. The expandable intervertebralimplant of claim 1, wherein first and second outer portions abut eachother when the expandable intervertebral implant is in the initialposition.
 12. An expandable intervertebral implant insertable into anintervertebral disc space, the expandable intervertebral implantcomprising: a first outer portion defining opposed ends spaced from eachother along a longitudinal direction that includes a first direction anda second direction opposite the first direction, the first outer portionfurther defining a first bone contacting surface, wherein the firstouter portion defines a first pair of first and second engagementsurfaces that are spaced from each other along the longitudinaldirection, and the first and second engagement surfaces of the firstpair are each sloped at a first angle with respect to the longitudinaldirection; a second outer portion defining opposed ends spaced from eachother along the longitudinal direction, the second outer portion furtherdefining a second bone contacting surface spaced from the first bonecontacting surface along a transverse direction that is substantiallyperpendicular to the longitudinal direction, wherein the second outerportion further defines a second pair of first and second engagementsurfaces that are spaced from each other along the longitudinaldirection, and the first and second engagement surfaces of the secondpair are each sloped at a second angle with respect to the longitudinaldirection; first and second side walls spaced from each other along alateral direction that is perpendicular to each of the transversedirection and the longitudinal direction, such that the first and secondpairs of first and second engagement surfaces and the first and secondside walls cooperate so as to define an internal space; and an innercore having at least a portion disposed in the internal space, the innercore defining a first pair of third and fourth engagement surfaces thatare aligned with each other along the longitudinal direction, and asecond pair of third and fourth engagement surfaces that are alignedwith each other along the longitudinal direction, wherein the third andfourth engagement surfaces of the first pair of third and fourthengagement surfaces are sloped at the first angle with respect to thelongitudinal direction, and the third and fourth engagement surfaces ofthe second pair of third and fourth engagement surfaces are sloped atthe second angle with respect to the longitudinal direction, wherein theinner core, including the first and second pairs of third and fourthengagement surfaces, is translatable in a straight path in the firstdirection relative to the first and second outer portions, so as tocause 1) the first and second engagement surfaces of the first pair offirst and second engagement surfaces to ride along the third and fourthengagement surfaces, respectively, of the first pair of third and fourthengagement surfaces, thereby deflecting the first outer portion awayfrom the second outer portion along the transverse direction and 2) thefirst and second engagement surfaces of the second pair of first andsecond engagement surfaces to ride along the third and fourth engagementsurfaces, respectively, of the second pair of third and fourthengagement surfaces, thereby deflecting second outer portion away fromthe first outer portion along the transverse direction, wherein thefirst outer portion and the second outer portion are prevented frommoving toward each other in response to a compressive force applied tothe first and second outer portions along the transverse direction whileboth 1) the first and second engagement surfaces of the first pair offirst and second engagement surfaces are in abutment with the third andfourth engagement surfaces, respectively, of the first pair of third andfourth engagement surfaces, and 2) the first and second engagementsurfaces of the second pair of first and second engagement surfaces arein abutment with the third and fourth engagement surfaces, respectively,of the second pair of third and fourth engagement surfaces, and whereinthe first and second bone contacting surfaces define an orientation withrespect to each other prior to deflection of the first and second outerportions away from each other, and the orientation remains constant asthe first and second outer portions deflect away from each other. 13.The expandable intervertebral implant of claim 12, wherein the first andsecond side walls are defined by the first and second outer portions.14. The expandable intervertebral implant of claim 12, furthercomprising a first member configured to abut the inner core and drivethe inner core to translate relative to the at least one of the firstand second outer portions in the first direction, the expandableintervertebral implant further comprising an elongate member thatextends from the first member and into a bore of the inner core.
 15. Theexpandable intervertebral implant of claim 14, wherein the elongatemember extends from the first member and into the inner core at a firstlongitudinal end of the inner core.
 16. The expandable intervertebralimplant of claim 15, wherein the elongate member extends away from theinner core at a second longitudinal end of the inner core that isopposite the first longitudinal end along the longitudinal direction.17. The expandable intervertebral implant of claim 14, furthercomprising a cylindrical body that defines an articulation surface thatis configured to receive the elongate member.
 18. An expandableintervertebral implant insertable into an intervertebral disc space, theexpandable intervertebral implant comprising: a first outer portiondefining opposed ends spaced from each other along a longitudinaldirection, the first outer portion further defining a first bonecontacting surface; a second outer portion defining opposed ends spacedfrom each other along the longitudinal direction, the second outerportion further defining a second bone contacting surface spaced fromthe first bone contacting surface along a transverse direction that issubstantially perpendicular to the longitudinal direction, wherein atleast one of the first and second outer portions further defines firstand second engagement surfaces that are spaced from each other along thelongitudinal direction; and an inner core disposed between the first andsecond outer portions, the inner core defining third and fourthengagement surfaces that are spaced from each other and aligned witheach other along the longitudinal direction, wherein the inner core isconfigured to receive a force in a forward direction that is orientedalong the longitudinal direction, such that the force drives the innercore, including the third and fourth engagement surfaces, to translatetogether in the forward direction relative to the at least one of thefirst and second outer portions, thereby causing the first and secondengagement surfaces to ride along the third and fourth engagementsurfaces, respectively, which in turn causes the at least one of thefirst and second outer portions to deflect away from the other of thefirst and second outer portions along the transverse direction; and anelongate member that is received in a bore of the inner core and extendsout from the inner core in the forward direction.
 19. The expandableintervertebral implant of claim 18, wherein the elongate member definesa portion that is aligned with each of the first and second outerportions prior to translation of the inner core in the forwarddirection, and the portion of the elongate member is offset from thefirst and second outer portions in the forward direction after the innercore has translated in the forward direction.
 20. The expandableintervertebral implant of claim 19, wherein the elongate membertranslates along with the inner core in the forward direction.
 21. Theexpandable intervertebral implant of claim 18, wherein the implantconsists of the elongate member and a remainder of the implant, and aportion of the elongate member extends out beyond the remainder of theimplant in the forward direction when the first and second outerportions have deflected away from the other of the first and secondouter portions along the transverse direction.
 22. The expandableintervertebral implant of claim 18, wherein each of the first, second,third and fourth engagement surfaces are substantially parallel to eachother and sloped with respect to the longitudinal direction.
 23. Theexpandable intervertebral implant of claim 22, wherein each of the firstand second outer portions further defines respective first and secondengagement surfaces that are spaced from each other along thelongitudinal direction, and the inner core includes first and secondpairs of third and fourth engagement surfaces, such that as the innercore translates in the first direction relative to each of the first andsecond outer portions, (i) the first and second engagement surfaces ofthe first outer portion ride along the third and fourth engagementsurfaces, respectively, of the first pair, and (ii) the first and secondengagement surfaces of the second outer portion ride along the third andfourth engagement surfaces, respectively, of the second pair.
 24. Theexpandable intervertebral implant of claim 23, wherein (i) each of thefirst and second engagement surfaces of the first outer portion and thethird and fourth engagement surfaces of the first pair are sloped withrespect to the longitudinal direction and are substantially parallel toeach other, and (ii) each of the first and second engagement surfaces ofthe second outer portion and the third and fourth engagement surfaces ofthe second pair are sloped with respect to the longitudinal directionand are substantially parallel to each other.
 25. The expandableintervertebral implant of claim 18, wherein the first outer portiondefines the first and second engagement surfaces, the second outerportion defines an inner engagement surface opposite the second bonecontacting surface along the transverse direction, the second outerportion includes teeth that project from the inner engagement surface,the inner core includes a plurality of teeth opposite the third andfourth engagement surfaces, respectively, along the transversedirection, and the teeth of the inner core are sized and shaped tointerlock with the teeth of the second outer portion.
 26. The expandableintervertebral implant of claim 18, wherein after the at least one ofthe first and second outer portions has deflected away from the other ofthe first and second outer portions along the transverse direction,both 1) the first and second engagement surfaces are in abutment withthe third and fourth engagement surfaces, respectively, and 2) the firstand second outer portions are prevented from moving toward each otheralong the transverse direction.
 27. An expandable intervertebral implantinsertable into an intervertebral disc space, the expandableintervertebral implant comprising: an outer member having opposed endsspaced from each other along a longitudinal direction that includes afirst direction and a second direction opposite the first direction, theouter member defining a first bone contacting surface and a second bonecontacting surface spaced from the first bone contacting surface along atransverse direction that is substantially perpendicular to thelongitudinal direction, wherein the outer member defines first andsecond engagement surfaces that are each sloped along the transversedirection as they extend along the longitudinal direction; an inner coredefining opposed ends spaced from each other along the longitudinaldirection, the inner core disposed between first and second outerportions of the outer member with respect to the transverse direction,the inner core defining third and fourth engagement surfaces that arealigned with each other along the longitudinal direction; and means fordriving the inner core, including the third and fourth engagementsurfaces together, to translate relative to the outer member in thefirst direction, such that the first and second engagement surfaces ridealong the third and fourth engagement surfaces, thereby causing theouter member to expand along the transverse direction from an initialposition to an expanded position, wherein a relative orientation betweenthe first and second bone contacting surfaces remains constant as theouter member expands along the transverse direction, and wherein whenthe outer member is in the expanded position, the outer member isprevented from moving from the expanded position to the initial positionin response to a compressive force applied to the outer member along thetransverse direction.